The genus Bathypterois Günther, 1878 comprises about 19 species of benthic deep-sea fishes commonly known as tripodfishes or spiderfishes (^{Davis & Chakrabarty, 2011}; ^{Eschmeyer & Fong, 2014}). These fishes are distributed worldwide in both temperate and tropical oceans and are found at depths up to 6000 m (^{Sulak, 1977}).

The Atlantic Ocean, with at least 9 valid species, appears to exhibit the highest diversity of tripodfishes (^{Davis & Chakrabarty, 2011}; ^{Eschmeyer & Fong, 2014}; ^{Franco, Braga, Nunan, & Costa, 2009}). In contrast, in the Eastern Pacific Ocean only 4 species of the genus have been formerly recorded (^{Castellanos-Galindo, Rubio-Rincón, Beltrán-Léon, & Baldwin, 2006}; ^{Castro-Aguirre & Balart, 1996}; ^{Eschmeyer & Fong, 2014}; ^{McCosker & Rosenblatt, 2010}; ^{Parin & Makushok, 1973}; ^{Pequeño, 1989}, ¹⁹⁹⁷, ²⁰⁰⁰; ^{Sulak, 1977}). The Eastern Pacific species are: (1) the attenuated spiderfish, B. atricolor Alcock, 1896, known from the gulf of California to Chile; (2) the abyssal spiderfish, B. longipes Günther, 1878, restricted to the Gulf of Panama; (3) the Southeastern Pacific spiderfish, B. pectinatus Mead, 1959, known from the Gulf of Panama to Chile; and (4) the ventrad spiderfish, B. ventralis Garman, 1899, known from the mouth of the Gulf of California to Chile (^{Castellanos-Galindo et al., 2006}; ^{Castro-Aguirre & Balart, 1996}; ^{Eschmeyer & Fong, 2014}; ^{McCosker & Rosenblatt, 2010}; ^{Parin & Makushok, 1973}; ^{Pequeño, 1989}, ¹⁹⁹⁷, ²⁰⁰⁰; ^{Sato, 2009}; ^{Sulak, 1977}). Despite the wide distribution of some of these species in Eastern Pacific waters, to date none of them have been formally listed among the Costa Rican Pacific ichthyofauna (^{Bussing & López, 1994}, ²⁰⁰⁵, ²⁰⁰⁹, ²⁰¹¹).

Between 1990 and 1992, 2 adult tripodfishes (110.3 and 128.3 mm in standard length [SL]; Fig. 1) were captured, independently, by commercial fishers from off the Pacific coast of Costa Rica (10°40′ N, 86°30′ W and 9°27′ N, 85°06′ W), at depths between 825 and 880 m and 637 and 665 m, respectively. These specimens were donated and deposited in the fish collection of the Museo de Zoología of the Universidad de Costa Rica (UCR) with the following catalog numbers: UCR 2199-001 and UCR 2290-03, respectively. Recently, both specimens were revised and identified as Bathypterois ventralis . In this contribution, we formally report this new record, the first for the species, the genus, and the family Ipnopidae in Costa Rican waters (^{Bussing & López, 1994}, ²⁰⁰⁵, ²⁰⁰⁹, ²⁰¹¹).

Figure 1 Bathypterois ventralis, 110.3mm in SL (UCR 2199-001; A) and 128.3mm in SL (UCR 2290-03; B), caught off Costa Rica (10°40′38.77″N, 86°30′30.48″W and 9°27′3.02″N, 85°6′33.44″W, respectively). Scale bar: 10mm. 

Identification of specimens was carried out on the basis of the following distinctive characters: body long and compressed, its depth 12.0-12.6% SL, dark brown, darker in the head, lighter at the margins of the scales and the lateral line; head moderately depressed and pointed at the snout; snout length 30.4-32.2% of head length (HL); lower jaw prominent; premaxilla and dentary each provided with a band of small conical pointed teeth; vomer with a patch of similar teeth on each knob; mouth wide and horizontal; eyes minute, its length 7.3-7.4% of HL; interorbital space moderate, 35.1-35.3% of HL; opercles thin, membranous, covered with scales; gill rakers long and bladelike, 45-46 on the first gill arch; scales deciduous, 58-59 in the lateral line; gular folds unscaled; pale brown fins; prepectoral length moderate, 23.9-25.0% of SL; pectoral, pelvic, and caudal fins with stiffened produced rays; the 2 produced pectoral rays (third and fourth rays) united at their base, but separate behind middle of the dorsal fin base; lower portion of pectoral fins with 14 rays; no pectinate scales behind the base of the pectoral fin; pelvic fins with 9 rays; dorsal fin inserted behind origin of pelvic fin; a very small adipose dorsal fin present; ventral procurrent rays modified to form a subcaudal notch; and caudal fin wide and deeply forked. All these characters agree with the diagnosis of the species and match well descriptions of specimens by ^{Garman (1899)}, ^{Sulak (1977)} and ^{Sato (2009)}. Other morphometric and meristic data from examined specimens and comparative information from all Eastern Pacific species of the genus are summarized in Table 1.

Table 1 Morphometric and meristic data of Bathypterois ventralis from Costa Rica (UCR 2199-001 and UCR 2290-03) and comparative material; data from ^{Garman (1899)}, ^{Sulak (1977)} and ^{Sato (2009)}. Morphometric data expressed as percentages of standar length. 

Measurements unavailable (i.e. structure broken or incomplete) are represented with an en-dash (-).

The biology of B. ventralis , a denizen of relatively great depths (637-1735 m), is poorly known, due almost certainly to scarcity of specimens and field observations. At the present time, according to ^{Sulak (1977)}, and to the FishBase (^{Froese & Pauly, 2014}), the Global Biodiversity Information Facility (GBIF: http://www.gbif.org/) and the FishNet2 (http://fishnet2.net/) online databases, less than 50 specimens of this species have been caught. Notably, all these specimens came from only 13 localities, 6 of them in Eastern Pacific waters (Fig. 2): (1) the mouth of the Gulf of California; (2) the central coast of México (^{Sulak, 1977}; ^{Castro-Aguirre & Balart, 1996}); (3) the gulf of Panama (^{Castellanos-Galindo et al., 2006}; ^{Sulak, 1977}); (4) the southern coast of Peru (^{Sulak, 1977}; ^{Sato, 2009}); (5) the northern, and (6) central coasts of Chile (^{Pequeño, 1989}, ¹⁹⁹⁷, ²⁰⁰⁰; ^{Sulak, 1977}).

Figure 2 Records of Bathypterois ventralis in the Eastern Pacific Ocean; stars=the present records (UCR 2199-001 and UCR 2290-03), squares=previous literature and museum records. Adapted from http://www.gbif.org. 

In recent years, an important number of fish species have been recorded for the first time in Costa Rican waters, mainly on the Pacific coast (^{Angulo, López, Bussing, & Murase 2014}; ^{Angulo, Naranjo-Elizondo, Corrales-Ugalde, & Cortés, 2014}; ^{Angulo, 2014a}, ^2014b; ^{Bussing & López, 2011}; ^{Cortés, Sánchez-Jiménez, Rodríguez-Arrieta, Quirós-Barrantes, González, & Blum, 2012}; ^{López-Garro, Zanella, Golfín-Duarte, & Pérez-Montero, 2012}; ^{Starr, Green, & Sala, 2012}). Some of these species are probably residents in these areas, undetected due to intrinsic rarity or difficulty of access to these specific habitats (e.g. deep sea), as in this case; others could be considered "vagrant" (i.e. they have arrived from the other areas), see ^{López-Garro et al. (2012)}. The presence of these previously unrecorded species indicates that the Costa Rican marine ichthyofauna is considerably richer and a reliable estimation of number, composition and distribution of species is still not available.

The expansion of fisheries into deeper waters and the development of new fisheries for new deepwater target species in this area (^{Wehrtmann & Nielsen-Muñoz, 2009}, for an overview) will likely bring new captures of unexpected species. As a result, some species currently considered rare, such as the one reported here, may turn out to be common or abundant at certain depths or habitats.

Finally, the discovery of these specimens of B. ventralis in Costa Rican waters increases the knowledge of our marine ichthyofauna and provides evidence of a broader distributional pattern for this species in the Eastern Pacific region, filling a gap of about 2600 km.

The authors are grateful to Ana Rosa Ramírez and the authorities of the Museo de Zoología of the Universidad de Costa Rica for encouragement and facilities. A.R. Vásquez and W. Valdelomar collected and donated the fish specimens to the UCR. A.A. and M.I.L. dedicate this work to the memory of William Bussing, who died on November 17, 2014, mentor, colleague, husband and friend.